In CAS systems, registration pointers are used in combination with trackable reference systems to digitize points of bodily elements for various purposes, such as obtaining 3D models of bones. A registration pointer is typically trackable in a working field of the CAS system, and is calibrated such that the position of a tip thereof is known as a function of the tracking thereof by the CAS system. The tip of the registration pointer contacts a surface to be digitized, and a registration command or operation from a surgeon will have the point of contact between the tip of the registration pointer and the surface registered.
Registration pointers have evolved so as to be provided with additional features. As an example, some types of pointers are provided with a pointed tip that can be used to perform perforations in soft tissue. Such a pointed tip not only reduces the invasiveness of the registration process of CAS, but also accelerates the surgical procedures by removing the step of performing a pre-registration incision. Such an additional feature is in line with important design factors of CAS: reduce the invasiveness of surgery, and accelerate surgical procedures. These design factors must be applied to all aspects of the registration pointers, including sterilization and calibration.
However, a problematic issue with pointed-tip registration pointers is that pointed tips can perforate organs and canals. For instance, in some orthopaedic CAS procedures such as hip replacement, registration points are frequently taken on the pelvis. For registration points taken on the pubic tubercle, there is a risk of perforating the urethra.